Impregnated electromagnetic coil having a layer voltage applied thereto

ABSTRACT

A novel electromagnetic coil is provided which is manufactured by placing and fixing an impregnable insulating material in such a manner that the insulating material contacts the whole surface of each side of an elementary electromagnetic coil consisting of a wire or self-bonding wire, to each side of which is applied a layer voltage, and then impregnating an impregnant into the elementary coil. The electromagnetic coil according to this invention ensures an improved working property in the manufacture of coils, reduction in manufacturing cost and an improved space factor.

United States Patent Shibano et al.

IMPREGNATED ELECTROMAGNETIC COIL HAVING A LAYER VOLTAGE APPLIED THERETOInventors: Takashi Shibano, Suita; Koichi Hirakawa, Kawanishi;Toshimitsu Yonehara, Takarazuka, all of Japan Assignee: MatsushitaElectric Industrial Co.,

Ltd., Kadoma-shi, Osaka, Japan Filed: Apr. 2, 1973 Appl. No.: 347,041

Foreign Application Priority Data Mar, 31, 1972 Japan 47-32781 U.S. Cl.335/297, 336/205 Int. Cl. HOlf 3/00 Field of Search 335/299, 282;336/205,

References Cited 7 UNITED STATES PATENTS DOrio 336/205 X Mar. 11, 19752,814,581 11/1957 Flynn 336/205 X Primary E.\'aminerG. Harris Attorney,Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A novelelectromagnetic coil is provided which is manufactured by placing andfixing an impregnable insulating material in such a manner that theinsulating material contacts the whole surface of each side of anelementary electromagnetic coil consisting of a wire or self-bondingwire, to each side of which is applied a layer voltage, and thenimpregnating an impregnant into the elementary coil. The electromagneticcoil according to this invention ensures an improved working property inthe manufacture of coils, reduction in manufacturing cost and animproved space factor.

4 Claims, 4 Drawing Figures PATENTEB 1 1975 3870.982

sum 2 0f 2 IMPREGNATED ELECTROMAGNETIC COIL HAVING A LAYER VOLTAGEAPPLIED THERETO The present invention relates to an electromagnetic coilhaving an improved insulating property and a method for manufacturingthe same.

Generally, heretofore known electromagnetic coils having an interlayerinsulating material disposed between all the layers have beenmanufactured employing various processes of applying insulatingmaterials, e.g., the varnishing process, the process of molding bypouring or impregnation or the use of a casing filled with an insulatingoil. These processes have been selectively employed depending on theapplications to which the coils are intended.

A drawback of these conventional electromagnetic coils is that the useof the interlayer insulating material causes a deteriorated workingproperty in the manufacture and moreover a low space factor of theelectromagnetic coil has prevented the realization of smaller and morecompact apparatus.

It is therefore an object of the present invention to minimize the useof interlayer insulating material in the manufacture of electromagneticcoils, thereby ensuring an improved working property in the productionof coils and a higher space factor.

According to the manufacturing method of this invention, it is possibleto provide an electromagnetic coil which has a good working property andwhich is compact and lighter, thereby making a great contribution towardimproving the productivity.

Other objects and advantages of this invention will be readily apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view of an elementary electromagnetic coilemployed with the present invention;

FIG. 2 is a partial perspective view of the elementary coil which hasbeen provided with an insulating material but not yet subjected to theprocess of impregnation;

FIG. 3 is a perspective view of another embodiment of the elementaryelectromagnetic coil of this invention which is composed of aself-bonding wire; and

FIG. 4 is a schematic diagram showing in crosssection the coils of FIG.2.

The present invention will be explained in greater detail with referenceto FIGS. 1 and 2.

FIG. 1 shows an elementary electromagnetic coil comprising a wire of thetype which is commonly used. In FIG. 1, numeral 1 designates a wirewhich is suitably selected depending on the actual operating temperatureof an apparatus and the environment in which 'it is used. Among Class Einsulating materials in terms of heat resisting properties, polyvinylformal wire has been used widely. Those which have slightly higher heatresisting properties include epoxy wire, polyester wire, etc.Polyesterimide wire, heat resistant polyester wire, polyimide wire,etc., have still higher heat resist ing properties. Numeral 2 designateslead wires which are normally used by connecting intermedially with aninsulated wire having reinforced mechanical and electric insulatingproperties. Numeral 3 designates an adhesive insulating tape. After thecompletion of the winding of the coil, the insulating tape 3 is providedon the coil at predetermined places to prevent the loosening of thecoil. It is essential that the properties of the insulating tape 3 aresuch that it possesses an excellent adaptability with the wire and othercomponent materials with which it contacts in the actual workingsurroundings. More particularly, Nomex (trademark for a heat-resistantnylon manufactured by E. I. du Pont de Nemours and Company) includingsilicone resin as an adhesive may be used advantageously, if the wirecornprises polyimide wire, polyesterimide wire or polyamideimide wireand if the varnish used to impregnate the electromagnetic coil comprisesepoxy resin, polyester resin or silicone resin. While the heat resistingproperties are slightly less favorable, glass cloth having an adhesive,e.g., epoxy resin applied thereon or Nomex using the similar resin as anadhesive may lend itself to be an excellent insulating tape, if the wirecomprises epoxy wire or polyester wire and if the varnish comprisessimilarly polyester resin, epoxy resin or phenol resin. However, it isnecessary to conduct tests on these materials in the presence of theassociated materials to confirm their reliability before putting them tothe actual use.

When the elementary coil has been prepared in the manner as abovedescribed, a readily impregnable insulating material is placed incontact with each of the sides of the elementary coil and a varnish orthe like is impregnated into the insulating material to reinforce theelectrical insulator strength of the coil sides.

In other words in FIG. 2 numeral 4 designates an insulating materialwhich is preferably such a porous material that a maximum contact areais ensured between the coil side and the insulating material. The reasonis that the wire at the coil side receives the voltage for two layersand the voltage increases as the distance between the coil side and theinsulating material increases, thus tending to cause corona discharge,surface tracking or arc discharge. These undesirable phenomena areavoided by closely fitting the insulating material to the coil sidesthereby preventing the formation of voids between the coil side and theinsulating sheet 4 and assuring that the effectiveness of an impregnantsubsequently applied to make the coil sides more dense is not impaired.Referring to the crosssectional diagram of FIG. 4, the wire segmentscomprising the coil 1 are designated by the numerals l to 24 and thelayers of the wound coil are indicated by the letters a to d. If avoltage V is applied across the coil, then the voltages impressedbetween the wires I and 2, 2 and 3 22 and 23, and 23 and 24 respectivelyv/24. The layer voltage appliedbetween the wires 1 and I2, 7 and 18 and13 and 24 is equal to l2/24V. That is, the layer voltage, which ishigher than the voltages between the wires, is applied between the coilsides.

To obtain better results from this effect, those materials which meetthe previously mentioned requirements should preferably be used.Materials which may produce an excellent effect include kao wool(ceramic fiber) which is made of kaolin, glass fiber mat, polyethyleneterephthalate nonwoven fabric, etc. When these materials are usedsingly, the insulating material does not fit tightly on the coil sidesand it is therefore necessary to use a highly resilient material 5 as asupporting material. Numeral 6 designates an insulating tape for tightlyfitting the materials 4 and 5 on the coil sides. Numeral 7 designates aninsulating material which is effective when a high electric field isapplied to the coil and its exterior and it is also essential that theinsulating material 7 is such that it fits tightly on the coil and isreadily impregnable so as to leave voids-free between the coil and theinsulating material 7. For this reason, a material having the similarproperty as the insulating sheet 4 may be preferred. If a layer of airis allowed between the insulating material 7 and the elementary coil,the corona discharge in the voids causes the breakdown of the insulatinglayer and shortens the life of the coil. A material having a goodelectrical insulating property and porosity may be suited for the highlyresilient material 5, since the porosity ensures an improvedimpregnation of the impregnant into the coil. More specifically,asbestos, porous sheet material and the like meet these essentialrequirements. However, the resilient material needs not always be ofporous nature. More specifically, it may be a molded plate of epoxyresin, polyester resin or phenol resin, or a laminated plate of glassfibers employing any of these resins.

The impregnating varnish may consist of epoxy resin, unsaturatedpolyester resin, silicone resin or the like, while mineral oil, siliconeoil or the like may provide a suitable liquid impregnant that may beemployed to impregnate the coil after it has been assembled in anapparatus and housed in a casing.

Further, the elementary wire shown in FIG. 1 may comprise a self-bondingwire 1' as shown in FIG. 3.

It is to be noted that an electromagnetic coil prepared by subjecting anelementary coil having the interlayer insulating material between someof the wire layers to the processes similar to those of the illustratedembodiment, also comes under the scope of this invention.

The electrical properties of the electromagnetic coil obtained in themanner so far described compare quite favorably with those ofconventional electromagnetic coils having the interlayer insulatingmaterial disposed between the wire layers. On the contrary, theelectromagnetic coil according to the present invention ensures animproved reliability and makes the process of product design easierowing to its simplified structure and the resultant decrease in thevariations of the electrical properties with different electromagneticcoils.

Further, the elimination of the use of interlayer insulating materialconsiderably improves the working property in the manufacture of coilsand it is also a great advantage from the standpoint of material cost.

Furthermore, a remarkable improvement in the space factor makes itpossible to achieve the ultimate object of the invention, i.e., therealization of more compact and lighter apparatus.

What is claimed is:

1. An electromagnetic coil comprising an elementary electromagnetic coilcomposed of a self-bonding electric wire wound in the form of aplurality of layers and having no interlayer insulating paper;impregnable ring-shaped insulating sheets closely fitted to and securedon each side of said elementary coil, to which a layer voltage isapplied, to allow said wire at each of said coil sides to be embedded inone of said insulating sheets; and a varnish impregnated and hardened insaid. elementary coil to make the electromagnetic coil voidfree betweensaid coil sides and said insulating sheets to prevent an arc dischargefrom being generated between coil layers along a surface of each of saidcoil sides.

2. An electromagnetic coil according to claim 1, further comprisinganother insulating sheet superimposed on said ring-shaped readilyimpregnable insulating sheet, said another insulating sheet having amechanical strength greater than that of said first insulating sheet,whereby a first insulating sheet is tightly fitted and secured on eachof said coil sides.

3. An electromagnetic coil according to claim 1, further including along and narrow insulating sheet consisting of a readily impregnablenonwoven fabric, said long and narrow insulating sheet being woundaround an outer surface of said coil, whereby the joints be-- tween saidfirst insulating sheet and said long and narrow insulating sheet aretightly connected and secured together.

4. An electromagnetic coil according to claim 2, wherein said firstinsulating sheet fitted on the coil sides to which the layer voltage isapplied and said another insulating sheet superimposed on said firstinsulating sheet are taped integrally with said coil, whereby said wireis embedded in said first insulating sheets.

1. An electromagnetic coil comprising an elementary electromagnetic coilcomposed of a self-bonding electric wire wound in the form of aplurality of layers and having no interlayer insulating paper;impregnable ring-shaped insulating sheets closely fitted to and securedon each side of said elementary coil, to which a layer voltage isapplied, to allow said wire at each of said coil sides to be embedded inone of said insulating sheets; and a varnish impregnated and hardened insaid elementary coil to make the electromagnetic coil void-free betweensaid coil sides and said insulating sheets to prevent an arc dischargefrom being generated between coil layers along a surface of each of saidcoil sides.
 1. An electromagnetic coil comprising an elementaryelectromagnetic coil composed of a self-bonding electric wire wound inthe form of a plurality of layers and having no interlayer insulatingpaper; impregnable ring-shaped insulating sheets closely fitted to andsecured on each side of said elementary coil, to which a layer voltageis applied, to allow said wire at each of said coil sides to be embeddedin one of said insulating sheets; and a varnish impregnated and hardenedin said elementary coil to make the electromagnetic coil void-freebetween said coil sides and said insulating sheets to prevent an arcdischarge from being generated between coil layers along a surface ofeach of said coil sides.
 2. An electromagnetic coil according to claim1, further comprising another insulating sheet superimposed on saidring-shaped readily impregnable insulating sheet, said anotherinsulating sheet having a mechanical strength greater than that of saidfirst insulating sheet, whereby a first insulating sheet is tightlyfitted and secured on each of said coil sides.
 3. An electromagneticcoil according to claim 1, further including a long and narrowinsulating sheet consisting of a readily impregnable nonwoven fabric,said long and narrow insulating sheet being wound around an outersurface of said coil, whereby thE joints between said first insulatingsheet and said long and narrow insulating sheet are tightly connectedand secured together.